1. Field of the Invention
The present invention generally relates to a lane recognizing image processing system for generating vehicle position information used in a motor vehicle control system such as typified by a lane keep system (LKS) or the like, which system is designed for ensuring precautionary safety for the operation of a motor vehicle by activating a lane departure warning system (LDWS) to thereby mitigate a burden otherwise imposed on the operator or driver of the motor vehicle.
2. Description of Related Art
In general, the object to be recognized by the lane recognizing image processing system is lane markings representing lane boundary lines which are applied or painted on a road in white or yellow. Of course, various forms of the lane markings are adopted in dependence on countries and/or localities. By way of example, in California in the United States of America, there exist freeways and prefectural or state roads on which linear arrays or rows of road rivets called Botts' dots, a sort of raised pavement markers, are laid.
The Botts' dots mentioned above (hereinafter also referred to as the dot when used in the singular) are realized each in the form of a circular rivet and are regularly laid on the road along the lane boundary lines. In driving a motor vehicle on the road on which the Botts' dots are laid, a reaction force applied to a steering mechanism of the motor vehicle or a sound generated when the rivet or the Botts' dot is ridden over is monitored by a control system.
In this conjunction, it is noted that when compared with the painted lane markings such as white lines and yellow lines, visibility of the Botts' dots lane markings is extremely poor because of low contrast between the Botts' dots lane markings and the road surface and because of discontinuity of the Botts' dots lane markings as viewed in the direction in which the motor vehicle is traveling, as a result of which not a little difficulty is encountered in the recognition of the lane by the image processing system.
Furthermore, in the case where the image recognition is performed by resorting to a same lane recognition algorithm as that for the ordinary lane marking recognition, there arises the necessity to discriminate the signals originating in the Botts' dots from noise for thereby separating the Botts' dot signal from the noise, which will incur increasingly in the load imposed on hardware and software designed for post-processing of the lane images picked-up.
Since the Botts' dots lane markings do not satisfy the conditions such as “continuity of the lane markings”, and “high contrast relative to the road surface” which are prerequisites for many lane recognition algorithms, some measures must be taken for ensuring the robust recognition of high accuracy and high reliability.
Such being the circumstances, the hitherto known or conventional lane recognizing image processing system is provided with a driving environment arithmetic means for arithmetically determining the lane marking position on the basis of edges of the image and an inhibiting means for disabling or inhibiting the driving environment arithmetic means, wherein abnormality of the image is detected by comparing a quantity resulting from the processing of edges with a reference value to thereby inhibit operation of the driving environment arithmetic means when the abnormality is detected. For more particulars, reference may have to be made to e.g. Japanese Patent Application Laid-Open Publication No. 113221/1997 (also referred to as JP-A-1997-113221).
In the conventional lane recognizing image processing system such as disclosed in JP-A-1977-113221, erroneous lane marking recognition is evaded by inhibiting the lane marking recognition on the basis of the quantity obtained by the edge processing when the motor vehicle is traveling on the roads on which the Botts' dots are laid as the lane markings. Consequently, the lane recognizing image processing system is constantly set to the state incapable of recognizing the lane markings on the Botts' dots-laid road, giving rise to a problem.
Further, as another lane recognizing image processing system known heretofore, there has been proposed such a system which is so arranged as to convert or transform an original image into an edge image by differentiating the original image and performs the Hough conversion on the edge image to thereby extract a group of straight line segments approximating arrays of feature points of the image, wherein the straight lines corresponding to the lane markings are selected from the group of the approximate straight lines on the basis of the width of the road. For more particulars, reference may have to be made to e.g. Japanese Patent Application Laid-Open Publication No. 158976/1991 (also referred to as JP-A-1991-158976).
With the lane recognizing image processing system disclosed in JP-A-1991-158976, it is difficult to realize the lane recognition with reasonable accuracy for the group of straight lines composed of edge points of only one dot in the case where the dot is of a circular form whose contour line does not extend in parallel with the lane boundary line even if the Hough conversion of high noise insusceptibility is resorted to.
In the lane recognizing image processing system described in JP-A-1991-158976, decision processing is executed for identifying the sort or type of the lane markings (e.g. broken line) by detecting broken portions in the edge point row, which is however ineffective for the dots laid discontinuously.
In general, although the ordinary painted lane marking extends in parallel with the lane boundary line, the contours of the dots are not always in parallel with the lane boundary line. Accordingly, when the lane marking candidate point position is set on the contour line of the dot, the result of the lane recognition will indicate the lane extending in the direction deviated or departed from the actual lane boundary line.
In the following, problems which the conventional lane recognizing image processing systems suffer will be examined in the concrete by referring to FIGS. 15 16(a), 16(b) and 16(c) of the accompanying drawings.
FIG. 15 is a perspective view for illustrating relations among Botts' dots 3, an approximate straight line L1 which approximates the lane, a lane boundary line L2 and lane marking candidate points C and shows that the approximate straight line L1 deviates or fluctuates by a half of the width of the Botts' dot 3 in the cases where the lane marking candidate points C on the Botts' dots 3 laid on a road at the left-hand side thereof are located inside of the lane.
FIGS. 16(a), 16(b) and 16(c) are views for illustrating relations among the Botts' dot 3, lane marking search or scanning lines 4 and the lane marking candidate point C and shows that the position of the lane marking candidate point C becomes different in dependence on the positional relation between the lane marking candidate point C and the lane marking search lines 4 on the assumption that the lane marking candidate point C on the Botts' dot 3 laid on the road at the left-hand side thereof is located inside of the lane.
As can be seen in FIGS. 16(a), 16(b) and 16(c), even when a plurality of the lane marking candidate points C on the Botts' dot 3 are used, the position and the number of the lane marking candidate points C on the Botts' dot 3 change in dependence on the positional relation between the lane marking search/scan lines 4 and the Botts' dot 3 and the resolution in the longitudinal direction in the case where the lane marking candidate points C are set at the positions inside of the lane relative to the Botts' dot 3 laid on the left-hand side. As a consequence of this, the result of the lane recognition contains departure of a magnitude equivalent to a half of the transverse width of the Botts' dot (lane marking) 3, as is shown in FIG. 15.
For evading occurrence of such departure, it is known to convert or transform the positions of the lane marking candidate points C not on the contour line of the Botts' dots 3 but on a straight line extending toward the null point (i.e., point at which the Botts' dot 3 makes disappearance) in accordance with a predetermined rule.
Certainly, the conversion method to this end will be practically effective so long as the method can be realized with low load imposed on hardware and software upon execution of the conversion.
However, even if the practically effective conversion method is adopted for solving the problem mentioned previously, the result of the lane recognition may nevertheless depart from the actual lane boundary line L2 in dependence on the accuracy and resolution of the conversion method when the lane marking candidate point(s) C exists only on the single dot 3.
Accordingly, there arises the necessity of determining that the lane marking candidate point (s) C exists only on the single dot. In this conjunction, it is however to be mentioned in conjunction with the decision as to existence of the lane marking candidate point(s) C only on the single dot 3 that the decision will result in that the recognition is impossible even in the case where approximation with a straight line interconnecting two Botts' dots 3 is possible when the decision is made on the basis of only the number of the candidate points, giving rise to a problem.
The problem of the unrecognizableness described above can certainly be coped with by making a decision on the basis of the inter-point distance between two points in the set of candidate points in the traveling direction of the motor vehicle. However, it will increase the cost involved in the arithmetic operation to check all possible combinations of the inter-point distances.
Further, the threshold value for determining the inter-point distance between the two points has to be so set that existence of the lane marking candidate points on the single Botts' dot 3 can be determined without fail.
In the case where existence of the lane marking candidate point(s) C only on the single dot 3 is ascertained, reliability of the information derived from the lane marking candidate point C is low. Accordingly, some countermeasures will have to be taken.
As the countermeasures to this end, there can be mentioned a method of invalidating the information derived from the lane marking candidate point C. This method is however disadvantageous in that the result of the lane recognition can not be referenced even when only one given frame becomes invalid in the course of traveling on the Botts' dots-laid road. Further, when the lane marking search is performed with reference to the result of the lane recognition obtained precedingly, speedy restoration of the lane recognition will become difficult.
Besides, the invalidation method mentioned above suffers an additional problem that when the result of the preceding lane recognition is being delivered as the output data notwithstanding that the result of the preceding lane recognition is erroneous, the output data of the erroneous recognition can not be corrected until the result of the succeeding lane recognition not invalidated is made available.
More concretely, when the result of the lane recognition is invalidated, the result of the preceding lane recognition or result of the time-based average processing can certainly be delivered as the output data. In that case, however, the period for which the result of the preceding lane recognition is to be held needs to be so set that the real time performance and the reliability are not thereby impaired.
As is apparent from the above, the conventional lane recognizing image processing system suffers a problem that when the lane marking candidate point C is located inside of the lane relative to the Botts' dot 3, as shown in FIGS. 16(a), 16(b) and 16(c), incoincidence of the position and the number of the lane marking candidate points C occurs among the individual Botts' dots 3, as a result of which departure corresponding to a half of the dot width is involved in the result of the lane recognition, as shown in FIG. 15.
Further, even if the above-mentioned problem is solved by the practically effective conversion method mentioned previously, the result of the lane recognition may depart from the actual lane boundary line when the lane marking candidate point(s) C exists only on the single dot 3. Accordingly, there arises the necessity of making decision as to whether the lane marking candidate point (s) C exists only on the single dot. However, when this decision is made on the basis of only the number of the lane marking candidate point(s) C, the decision may result in that the recognition is impossible even if approximation with a straight line interconnecting the two dot points 3 is possible, giving rise to a problem.
The problem mentioned just above can certainly be coped with by making a decision on the basis of the inter-point distance between the two points in the candidate point sets in the traveling direction. However, this solution will incur increased cost in the arithmetic operation because all possible combinations of the inter-point distances have to be referenced.
Further, in the case where existence of the lane marking candidate only on the single dot 3 is made apparent, the information of low reliability derived from this lane marking candidate is invalidated. This method is however disadvantageous in that the result of the lane recognition can not be referenced even in the case where only one given frame is rendered invalid in the course of traveling on the Botts' dots-laid road.
Further, when the lane marking search is performed with reference to the result of the lane recognition obtained precedingly, difficulty is encountered in the speedy restoration of the lane recognition.
Besides, the invalidation method mentioned above suffers an additional problem that when the result of the preceding lane recognition is being delivered as the output data notwithstanding that the result of the preceding lane recognition is erroneous, the output data of the erroneous recognition can not be corrected until the result of the succeeding valid lane recognition becomes available.